Filter

Abstract

A filter includes a piezoelectric film including lithium niobate or lithium tantalate, an acoustic wave resonator including a functional electrode on the piezoelectric film, a capacitor on the piezoelectric film and connected in parallel to the acoustic wave resonator, and a resonator electrically connected to the acoustic wave resonator. The functional electrode includes a pair of first and second electrodes facing each other in a direction intersecting a thickness direction of the piezoelectric film. When a thickness of the piezoelectric film is d and a center-to-center distance between the first electrode and the second electrode is p, d/p is smaller than or equal to about 0.5.

What is claimed is: 
     
       1. A filter comprising:
 a support substrate including a cavity portion and a support portion; 
 a piezoelectric film including lithium niobate or lithium tantalate; 
 an acoustic wave resonator including a functional electrode on the piezoelectric film; 
 a capacitor on the piezoelectric film and connected in parallel to the acoustic wave resonator; and 
 a resonator electrically connected to the acoustic wave resonator; wherein 
 the support portion supports the piezoelectric film; 
 the functional electrode includes at least one pair of a first electrode and a second electrode; 
 the at least one pair of the first electrode and the second electrode face each other in a direction intersecting a thickness direction of the piezoelectric film; and 
 when a thickness of the piezoelectric film is d and a center-to-center distance between the first electrode and the second electrode is p, d/p is smaller than or equal to about 0.5. 
 
     
     
       2. The filter according to  claim 1 , wherein the capacitor includes a first comb-shaped electrode on the piezoelectric film and electrically connected to the first electrode and a second comb-shaped electrode on the piezoelectric film, electrically connected to the second electrode, and interdigitated with the first comb-shaped electrode. 
     
     
       3. The filter according to  claim 1 , wherein an electrode electrically connecting the capacitor and the second electrode to each other is superposed on the support portion in plan view. 
     
     
       4. The filter according to  claim 1 , wherein the acoustic wave resonator is a series arm resonator or a parallel arm resonator, and the filter is a ladder filter. 
     
     
       5. The filter according to  claim 1 , wherein
 Euler angles (φ, θ, ψ) of a lithium niobate film or a lithium tantalate film of the piezoelectric film fall within a range of expression (1), expression (2), or expression (3) below:
   (0°+10°, 0 to 20°, any ψ)  expression (1);
 
   (0°±10°, 20 to 80°, 0 to 60°(1−(θ−50) 2 /900) 1/2 ) or (0°±10°, 20 to 80°, [180°−60°(1−(ψ−50) 2 /900) 1/2 ] to 180°  expression (2); and
 
   (0°±10°, [180°−30°(1−(ψ−90) 2 /8100) 1/2 ] to 180°, any ψ)  expression (3).
 
 
 
     
     
       6. The filter according to  claim 1 , wherein the acoustic wave resonator utilizes a bulk wave in a thickness slip mode. 
     
     
       7. The filter according to  claim 1 , wherein d/p is smaller than or equal to about 0.24. 
     
     
       8. The filter according to  claim 1 , wherein a thickness of the piezoelectric film is greater than or equal to about 40 nm and smaller than or equal to about 1000 nm. 
     
     
       9. The filter according to  claim 1 , wherein the at least one pair of the first electrode and the second electrode face each other in a direction orthogonal or substantially orthogonal the thickness direction of the piezoelectric film. 
     
     
       10. The filter according to  claim 1 , wherein the functional electrode is an interdigital transducer electrode. 
     
     
       11. The filter according to  claim 1 , wherein the functional electrode includes Al or an AlCu alloy. 
     
     
       12. The filter according to  claim 1 , wherein
 the functional electrode includes an AlCu alloy; and 
 a Cu content in an AlCu alloy is greater than or equal to about 1 weight % and smaller than or equal to about 20 weight %. 
 
     
     
       13. A filter comprising:
 a piezoelectric film including lithium niobate or lithium tantalate; 
 an acoustic wave resonator including a functional electrode on the piezoelectric film; 
 a capacitor on the piezoelectric film and connected in parallel to the acoustic wave resonator; and 
 a resonator electrically connected to the acoustic wave resonator; wherein 
 the functional electrode includes at least one pair of a first electrode and a second electrode; 
 the at least one pair of the first electrode and the second electrode face each other in a direction intersecting a thickness direction of the piezoelectric film; 
 when a thickness of the piezoelectric film is d and a center-to-center distance between the first electrode and the second electrode is p, d/p is smaller than or equal to about 0.5; 
 the functional electrode includes a first busbar and a second busbar that face each other; 
 the first electrode is connected to the first busbar, and the second electrode is connected to the second busbar; and 
 the capacitor includes the first busbar, an insulation film on the first busbar, and a capacitance electrode on the insulation film and electrically insulated from the first busbar. 
 
     
     
       14. The filter according to  claim 13 , wherein the first electrode and the second electrode are surrounded by an electrode electrically connecting the capacitor and the second busbar to each other, the first busbar, and the second busbar. 
     
     
       15. The filter according to  claim 14 , further comprising:
 a first connection electrode and a second connection electrode on the piezoelectric film and electrically connecting the capacitance electrode and the second busbar to each other; 
 wherein the first electrode and the second electrode are surrounded by the first busbar, the second busbar, the first connection electrode, and the second connection electrode. 
 
     
     
       16. The filter according to  claim 13 , wherein
 the capacitor is a first capacitor; 
 the filter further includes a second capacitor; and 
 the second capacitor includes a first comb-shaped electrode on the piezoelectric film and electrically connected to the first busbar and a second comb-shaped electrode on the piezoelectric film, electrically connected to the second busbar and the second electrode, and interdigitated with the first comb-shaped electrode. 
 
     
     
       17. The filter according to  claim 13 , wherein the insulation film includes an inclined portion. 
     
     
       18. The filter according to  claim 13 , wherein the insulation film covers one end portion of the first busbar, and does not cover another end of the first busbar. 
     
     
       19. A filter comprising:
 a piezoelectric film including lithium niobate or lithium tantalate; 
 an acoustic wave resonator including a functional electrode on the piezoelectric film; 
 a capacitor on the piezoelectric film and connected in parallel to the acoustic wave resonator; 
 a resonator electrically connected to the acoustic wave resonator; and 
 an acoustic reflective film; wherein 
 the functional electrode includes at least one pair of a first electrode and a second electrode; 
 the at least one pair of the first electrode and the second electrode face each other in a direction intersecting a thickness direction of the piezoelectric film; 
 when a thickness of the piezoelectric film is d and a center-to-center distance between the first electrode and the second electrode is p, d/p is smaller than or equal to about 0.5; 
 the piezoelectric film is on the acoustic reflective film; 
 the acoustic reflective film includes at least one low acoustic impedance layer having a relatively low acoustic impedance and at least one high acoustic impedance layer having a relatively high acoustic impedance; and 
 the low acoustic impedance layer and the high acoustic impedance layer are laminated in an alternating sequence.